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Francesco Ferrini Workshop

Research projects to improve growth and stress tolerance in the nursery and after transplanting in the urban environment

Francesco Ferrini

Department of Agrifood Production and Environmental Sciences – University of Florence, Viale delle Idee, 30 Sesto Fiorentino (Florence) Italy


The urban environment constrains tree growth and survival: drought, poor soil quality, soil compaction, light heterogeneity, transplant shock, pollutants, salinity, pathogens and conflicts with human activities often cause premature plant death, thus reducing the net benefit by urban green areas. It is therefore important to better understand the dynamics leading to tree decline in the urban environment, and to develop strategies and techniques aimed at improving the horticultural tolerance (i.e.the capacity to provide benefits, not only to survive, under stressful conditions) of urban trees. These include nursery preconditioning techniques and post-planting management techniques, but a key role is played by species selection. Hundreds of species are used in the urban environment, but selection criteria are frequently based upon aesthetics and whether the species are native or not, rather than on the tolerance to typical stresses imposed by the built environment and on the capacity to provide substantial benefits therein.This has lead to only a limited knowledge about the ecophysiology of shade trees, if compared to fruit trees and crop species. Research in the area of tree selection for tolerance of urban conditions so that the service life of trees in our communities is extended and the benefits provided by trees are maximized is limited in Europe. Therefore, tolerance mechanisms of species with validated and potential ornamental use, and cultural techniques for either pre-conditioning plants in the nursery or alleviating stress after planting are not very well-known.

Management choices related to species composition and types of tree maintenance activities can also directly affect the overall carbon benefits derived from urban forests. Therefore, planting trees requires special consideration regarding potential adverse factors to ensure the health of the trees, including a proper watering regime and adequate space. Limited water resources can be a big issue in the future, especially in the Mediterranean-like climate areas. In these areas trees will continue to provide many benefits if they are chosen according to the present and future conditions and are properly maintained.

Climate change is a scientific certainty and cities will be exposed to climate stresses which will involve higher temperature, lower air humidity and soil water availability, as well as higher levels of air pollutants. Effects of climate change are already detectable and will be more evident in the next 40 years. Rapid increases in human population and economic development have led to tremendous urbanization: more than 50% of the world human beings is now living in an urban area and 70% will do that in the year 2050, but urban areas are estimated to be less than a mere 3% of the total land of our planet. As more people's lives are predominantly urban,opportunities for interaction with the natural world decrease, with potentially serious effects for human health and well being. An urban area is a living complex mega-organism, associated with a lot of inputs, transformations, and outputs: heat, energy, materials, and others. Urban activities have now become a threat to the global environment. Solving and mitigating problems, including the design of ecologically efficient urban areas, is therefore of prime importance. Trees are essential in the urban environment not only because of their aesthetic and social values, but also for their effects on air quality.Trees offer double benefits: first by directly sequestering and storing atmospheric C and other pollutants; second, by providing a natural cooling mechanism through evapotranspiration and shade, green space dissipate solar energy that would otherwise be absorbed, so reducing air-conditioning energy needs and avoiding pollutant emissions. These abilities are counteracted by pollutant toxicity and adverse environmental conditions. Urban vegetation is often subjected to more extreme environmental conditions than vegetation of the peri-urban and rural areas. These conditions are related not only to higher atmospheric pollution levels caused by traffic and other anthropogenic emissions, but also to limiting water availability and higher temperatures,typical of the city micro climate. Due to the negative prospects for the urban environment caused by global climatic change, there is a need to monitor and manage pro-actively urban greening and peri-urban forests and to gather more basic data about urban trees, and urban green in general.


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